Solar cells are recently rapidly become popular because the cells do not emit carbon dioxide during the generation of electricity and are more environment-friendly.
Solar cell modules typically include a photovoltaic element (cell) disposed between a top surface glass, on which solar light is incident and a backsheet for a solar cell (hereinafter simply referred to as “backsheet”) on the opposite side of the side on which solar light is incident (on the backside). The solar cell modules include an encapsulant such as an ethylene-vinyl acetate (EVA) resin in a space between the top surface glass and the cell and a space between the cell and the backsheet.
The backsheet acts to prevent intrusion of moisture from the backside of a solar cell module. Although glass, fluorinated resin, and the like have been conventionally used for the backsheet, polyester is increasingly used in view of cost reduction.
A backsheet may be more than a mere polymer sheet and may be provided with various functions. For example, a white layer may be provided to the backsheet to provide higher reflectance, thereby using the reflected light to improve efficiency of power generation, or a pigmented blue or black layer is disposed to improve design (See, for example, Japanese Patent Application Laid-Open (JP-A) No. 2010-93120). As described above, it is advantageous to provide a layer to which a white or colored inorganic pigment has been added in view of assuring adequate reflectivity and design.
On the other hand, a backsheet should have good adhesion to an encapsulant. Especially, the backsheet should not separating from an encapsulant even after long storage under damp heat atmosphere, because the solar cell modules are installed outdoor.
JP-A No. 2000-243999 discloses a technique for improving adhesion by corona discharge treatment.
JP-A No. 2011-146658 discloses a backsheet including, on a polymer substrate, a colored layer which includes binder and a specified amount of pigment; and a readily adherable layer which includes a specified amount of binder and inorganic fine particles.
JP-A No. 2011-146659 discloses a backsheet film formed by applying, to a substrate film, an aqueous composition for a white layer including a white pigment, an aqueous binder, and an inorganic oxide filler, and an aqueous composition for an adhesive protective layer including an aqueous binder to form the white layer and the adhesive protective layer, respectively.